I don’t believe the distinction between full-time professional and part-time professional or amateur is really apt in music, or most arts, really, when it comes to deciding matters of skill.
Outside of the field consisting of performers of art music/serious music (insert whatever out-of-date term you like), lots of pros in rock, and jazz, for instance, have the reputation of being hacks. This isn’t just because there are loads of weekend warriors who might have superior instrumental skills, but rather that, on the one hand, scuffling for gigs often forces the musician of average skill to accept wedding jobs, corporate parties, cocktail hours, and, on the other hand, the set of skills a musician develops as a professional, as opposed to an amateur are largely extra-musical. Glad-handing, promoting, having the tux pressed, obsessing over the live rig, fixing the PA, printing an extra set of lead sheets, etc.
Anyway, I don’t know a single musician who doesn’t get paid occasionally to perform, whatever their level of employment elsewhere (including a private income, which I’d consider a “straight job”).
The distinction works much better for sports, where the line is more firmly drawn. 9-Ball is indeed an excellent example of a situation where the pros really lean on the kind of experience one only gets from playing the game against really deep opponents.